2.4.9 Sequence Manipulation Functions

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2 The SQL Language : 2.4 Functions and Operators : 2.4.9 Sequence Manipulation Functions

This section describes Advanced Server’s functions for operating on sequence objects. Sequence objects (also called sequence generators or just sequences) are special single-row tables created with the CREATE SEQUENCE command. A sequence object is usually used to generate unique identifiers for rows of a table. The sequence functions, listed below, provide simple, multiuser-safe methods for obtaining successive sequence values from sequence objects.
sequence.NEXTVAL
sequence.CURRVAL
sequence is the identifier assigned to the sequence in the CREATE SEQUENCE command. The following describes the usage of these functions.
Return the value most recently obtained by NEXTVAL for this sequence in the current session. (An error is reported if NEXTVAL has never been called for this sequence in this session.) Notice that because this is returning a session-local value, it gives a predictable answer whether or not other sessions have executed NEXTVAL since the current session did.
If a sequence object has been created with default parameters, NEXTVAL calls on it will return successive values beginning with 1. Other behaviors can be obtained by using special parameters in the CREATE SEQUENCE command.
Important: To avoid blocking of concurrent transactions that obtain numbers from the same sequence, a NEXTVAL operation is never rolled back; that is, once a value has been fetched it is considered used, even if the transaction that did the NEXTVAL later aborts. This means that aborted transactions may leave unused "holes" in the sequence of assigned values.

2 The SQL Language : 2.4 Functions and Operators : 2.4.9 Sequence Manipulation Functions

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